The use of electric vehicles (EVs) has been promoted in recent years to reduce oil consumption and the emissions of harmful pollutants and carbon dioxide. EVs may include battery powered vehicles, fuel cell powered vehicles, and hybrid electric vehicles (HEVs). Commercially available HEVs employ a battery and an electrical motor that are sized to optimize the energy efficiency of an internal combustion engine and to capture a portion of the kinetic energy for later use through dynamic braking by the motor during deceleration. As such, the batteries can only provide a very limited driving distance (a few miles) in the electrical only mode, in which the engine is not used. On the other hand, plug-in hybrids use a substantially larger battery to enable a driving distance of 20 to 60 miles for normal commuting in the all-electric mode after fully charged. To avoid fuel consumption and air pollutions by operating the engine, the battery is fully charged by a standalone external charger powered by the utility grid and the charging is done preferably overnight to leverage energy costs by taking advantage of off-peak electricity rates. Plug-in hybrids thus offer a greater potential than those hybrid vehicles currently available on the market to reduce oil consumption and the emissions of pollutants and carbon dioxide.
HEVs can have a variety of electrical motor drive systems and use different coupling mechanisms to combine the propulsion forces from an engine and the electrical motor(s) to drive the wheels. An electrical motor drive system may include an energy storage device and one or more drive units. A drive unit typically consists of a power inverter/converter and a motor, in which the inverter/converter either functions as an inverter to convert a dc voltage to an ac voltage suitable to operate the motor, or a converter when the motor is operating in power generation mode. Multiple electrical drive units can be used to provide four-wheel drive capabilities.
As an example, FIG. 1 illustrates a simplified block diagram of a parallel configuration HEV. It employs a single motor drive unit, whose electric motor is connected to the engine shaft through a mechanical transmission and works in parallel with the engine to provide propulsion force to the wheels (not shown in the figure) of the vehicle. The vehicle can be propelled by the engine alone, by the electrical motor alone (all-electric mode), or by both (hybrid mode). The electric motor, controlled by a power inverter/converter and powered by a high voltage (H.V.) battery, can provide the sole driving force in the all-electric mode, where the engine is disconnected from the transmission by the clutch. Or in hybrid mode, the motor handles the variations in the driving force demand to optimize the fuel efficiency of the engine. The motor is also used to start the engine and to charge the H.V. battery when needed during vehicle operations. For charging the battery, the motor functions as a generator driven by the engine or by the vehicle inertia during deceleration and produces an ac voltage, which is converted to dc by the power converter to supply the H.V. dc bus. An electronic controller based on one or more microprocessors is used to control the operations of the engine and electrical motor drive system.
It is desirable to have a large capacity battery being able to store energy enough to power the HEV for a driving distance long enough for a typical daily commuting without using the engine at all, and to be able to charge the battery by plugging into the grid through the charging socket. Traditionally this is accomplished by using a standalone battery charger, typically consisting of an inductor, a rectifier and a dc-to-dc converter to regulate a dc voltage across the dc bus for charging the battery. The standalone charger may be assembled into a single unit installed onboard or off-board the vehicle. Or it may be constructed into two pieces by separating the primary and secondary magnetic cores and windings of a transformer (as disclosed in U.S. Pat. Nos. 5,264,776 and 5,463,303) with one onboard and the other off-board the vehicle. When the two pieces are brought together power can be transferred from the ac source to the battery across the transformer.
An onboard battery charger can also be realized by using the electrical drive inverter and motor in an HEV. In a disclosure (Japanese patent P2000-232737A), a charging device was disclosed, which uses two additional diodes and the electrical motor and inverter to charge the battery from the utility grid. This device, however, cannot operate as a power source to supply external loads.
It is also desirable to make EVs/HEVs to be able to function as mobile electrical power generators for emergency and other uses. While battery-engine hybrids may be suitable for emergency needs, fuel cell powered vehicles may even be suited for regular uses because fuel cells do not generate air-polluting by-products. In a disclosure (US 2004/0062059 A1), an apparatus and method was disclosed to charge a battery in a fuel cell powered inverter-motor drive system or to make the drive system an electrical power source. It employs two switches to selectively couple a three-phase inverter to an electrical motor for operating the motor or to an ac power source through an additional inductor/filter for charging the battery with or without an optional “boosting circuit”.
It is now desirable to eliminate or minimize the number of additional components by integrating the battery charging function into the electrical motor drive systems to minimize the cost. The present invention presents hybrid electric vehicle systems and methods for battery charging and/or supplying electrical power to external loads. It is done by utilizing only the already onboard inverter(s) and motor(s) without adding any inductors or switches. Therefore, the present invention can fulfill all the requirements while not incurring any additional cost.